1. Field of the Invention
The present invention relates to the field of computer networks and more particularly to methods and apparatus for determining the load on a server in a distributed network such as the internet.
2. Description of the Related Art
Determining network loads on devices such as servers in a network is an integral function of network management. Traditionally, the load on a particular server in a network may be determined by proprietary network management software designed to manage the particular server. This information is available to a network administrator responsible for the server, but is not easily discoverable by any interested person.
It is desirable to discover server load information without access to specialized network management software designed for a particular server. If this information was available, it might be used, for example to explain delays in receiving responses at a client.
Network servers operating in accordance with standard IP protocols send IP datagrams to clients. The IP datagrams include an identification field (referred to herein as the IPID field) which provides a monotonically increasing value assigned to each IP datagram transmitted by the server. The IPID is designed to be used to allow for reassembly of packets. In certain cases, IP datagrams may have to be broken up or fragmented due to their overall length. All IP data fragments associated with a particular datagram are assigned the same IPID. Reassembly of the fragments is based on IPID.
FIG. 1 illustrates a typical transmission session between server and a client using the IP network layer protocol. Systems that originate IP datagrams must ensure that IPID is carefully selected to facilitate reassembly. One common practice is to start IPID at a random value in the range of 0 to 65,536 and increment the IPID by one for each IP datagram that is transmitted by the system. All intermediate devices which transmit the IP datagram are required to preserve the IPID field.
In one prior art approach, the IPID is utilized to perform offline analysis of a network.